Preparation

Bring 2 cups water, garlic, and 1 teaspoon sea salt to a boil, then drain in a colander. Blanch garlic in same manner 2 more times.

Cut bread into 1/4-inch-thick sticks and toast on a baking sheet in middle of oven until pale golden, about 6 minutes. Leave oven on.

Peel stems of porcini with a sharp small knife just until white flesh is exposed, then quarter mushrooms lengthwise.

Pat squabs dry and season generously inside and out with salt and pepper. Put a sprig of thyme in cavity of each squab and divide garlic confit among cavities. Tie legs of squabs together with kitchen string and fold wings back.

Heat 2 tablespoons duck fat in a well-seasoned 10-inch cast-iron skillet over moderately high heat until hot but not smoking, then brown squabs in 2 batches, turning, about 5 minutes, transferring to a plate and reserving skillet.

Add 1 1/2 more tablespoons duck fat to skillet and sauté porcini in 2 batches over moderately high heat, stirring occasionally, until golden brown, about 3 minutes (add another 1 1/2 tablespoons duck fat to skillet for second batch). Stir in blanched garlic, toasted bread, and salt and pepper to taste and remove from heat.

Cooks' notes:
 Squabs may be stuffed and tied 1 day ahead and chilled, covered. Pat dry just before browning.
 Bread may be toasted 2 days ahead, cooled completely, and kept in an airtight container at room temperature.